Classification of Rocks. 3 



it is needful that I should first enter on some rudimen- 

 tary points, so as to make the remainder intelligible to 

 all. Therefore I begin with an account of the nature 

 of rocks; because it is impossible to understand the 

 causes that produced the various kinds of scenery of 

 our country, and to account for the classification of its 

 mountains and plains, without first explaining the na- 

 ture of the rocks which compose them. 



To this will be added a concise account of the British 

 strata in serial order, that the reader may understand 

 something of the nature and history of the various 

 stratified formations which, together with igneous rocks, 

 form our island. 



In doing this I will endeavour to get and to give 

 some idea of the scenery of our region during the 

 successive geological epochs, so as to give the reader 

 some glimpses of those older stages of physical geo- 

 graphy, each of which in its time, had man been there 

 to see it, would have seemed as enduring as that passing 

 phase of the Earth's history in the midst of which we 

 live. 



All rocks, in the broadest sense, are divided into 

 two great classes AQUEOUS and IGNEOUS ; and there ih 

 a sub-class, which mostly consists of aqueous, but 

 sometimes of igneous rocks that have been altered, 

 and which in their characters often approach and even 

 by insensible gradations pass into some of those rocks 

 that are termed igneous, though in many respects very 

 different from ordinary volcanic products such as lavas. 

 In this chapter I shall, however, confine myself to a 

 general description of the two great classes of rocks, 

 those of aqueous or watery origin, and to those easily 

 recognised as of igneous origin, which are products of 

 subterranean heat. 



B 2 



